Conventionally, an energy storage device is known which is provided with an electrode assembly including, for example, a sheet-like positive electrode and a sheet-like negative electrode.
In this type of energy storage device, for example, each of the positive electrode and the negative electrode includes a sheet-like current collecting substrate and an active material layer disposed on at least one side of the current collecting substrate. Then, the electrode assembly is formed by, for example, winding of the positive electrode and the negative electrode facing each other.
In this electrode assembly, for example, the positive electrode and the negative electrode are layered by the winding and the positive electrode and the negative electrode are disposed so as to be alternately arranged in a layered direction. In addition, for example, the electrode assembly includes extension portions which are respectively formed on both sides in an axial direction of a winding axis (width direction of the sheet-like electrode) in such a manner that the current collecting substrate of the positive electrode and the current collecting substrate of the negative electrode extend outward more than an active material layer in a direction opposite to each other.
In such an energy storage device, for example, each of the extension portions includes a bundle portion formed by bundling the extended current collecting substrates of the electrodes at a leading end in an extending direction, and the bundle portion is disposed at a central portion of a thickness of the extension portion in the layered direction.
Then, the above energy storage device is configured such that the bundle portion acts as an electric path at charge-discharge of the energy storage device.
For example, WO 2011/016243 A proposes the kind of energy storage device provided with a negative electrode formed by cutting of a wide negative electrode plate (an original negative electrode plate) including a sheet-like current collecting substrate.
In the energy storage device disclosed in WO 2011/016243 A, the negative electrode is formed in such a manner that the wide electrode plate (wide negative electrode plate) including the sheet-like current collecting substrate and an active material layer disposed on at least one side of the current collecting substrate is cut in a thickness direction. Accordingly, at least a part of the end portion of the negative electrode includes a bent end portion at which the current collecting substrate is bent by cutting force.
The bent end portion of the negative electrode is formed by the cutting force applied to one side in the thickness direction during the cutting of the wide negative electrode plate. Thus, at the bent end portion of the negative electrode, the current collecting substrate is bent toward one side in the thickness direction of the negative electrode.
In this way, the energy storage device disclosed in WO 2011/016243 A is provided with the negative electrode of which the current collecting substrate is bent at the bent end portion. The energy storage device disclosed in WO 2011/016243 A has excellent manufacturing efficiency in that a plurality of negative electrodes are produced by the cutting of the wide negative electrode plate, as compared to the energy storage device provided with the negative electrode produced one by one.